JPP had a strange problem after his Panther install. Once he had finished his configuration and software installation, the "C" key of his keyboard started not working. After many discussions and many checks, he eventually found the origin of the problem: the software known as CopyPaste 1.6B5.

[robg adds: This was discussed on a few other boards around the web as well, so I thought it bore mentioning. There's also a workaround from Lauren R in this thread on the Apple Discussions site:

The problem is a conflict with the use of the COMMAND key preference that CopyPaste relies on - it is this that disables your "c".
Start CopyPaste and immediately go to the Preferences Menu. If you change the first popup preference to NOT use the COMMAND key, it will enable the "c" to work. The next TWO settings have to have a selection other than "no clip archive." Be careful not to select a shortcut that conflicts with other application shortcuts if you have had no clip archive selected previously. For example, cmd-shift-V will conflict with an Entourage shortcut to paste as quotation.

I don't have CopyPaste installed, so I can't verify either the problem or the fix, but others have claimed it worked.]